Music for the Article
The Heavy is the villain whose actions drive the plot. One of the things that an average viewer has seen a million times.
This is a dominant role for an actor, frequently the largest role in a play or movie. The term, which goes back to theater in the 1800s, may refer to this player having the heaviest script.
In modern times the heavy can also the villian who has the most presence in the story
For example Sauron is the Big Bad of Lord of the Rings, but Saruman (and to an extent the Witch-King and the other Ringwraiths) are much more visible and involved villains, especially in the movies. The One Ring itself is more active and visible than Sauron. Sauron doesn't even really appear himself, ever. Gollum is more of an actual presence than the Big Bad!
In some cases they can actually be the Big Bad, but is more often The Commander, since keeping the Big Bad mysterious generally makes him scarier. This is especially true in the case of a Non-Action Big Bad. An example in the original Star Wars trilogy, Emperor Palpatine may be the Big Bad, but Darth Vader is The Heavy. He's seen more. He has more to do. He dominates the films, and as the prequels prove, the story is about him.
Dispite the role seeming simple they are actually Very Dangerous
They tend to be self-proclaimed tyrants and would-be Galactic Conqueror.
A user and abuser of his followers they divide the world into enemies and pawns, destroying or enslaving the former, and ruthlessly exploiting the latter. They demonstrate some sadistic tendencies, considers his own allies expendable, and hopes to bring world, and eventually the galaxy, under his heel.
They will not hesatate to wipe out an entire nation just so he could absorb the souls of every citizen.
They are also not above sacrificing all of their remaining troops in order to gain control of an anchient doomsday weapon and set out to overrun the galaxy.